Callialaria curvicaulis is similar to Cratoneuron filicinum in many aspects, such as the broadly ovate to ovate-lanceolate stem leaves, the serrulate leaf margins, the hyaline and inflated alar cells, the nearly percurrent leaf costa, and the dioicous plants. Ochyra (1989) regarded these characters as being highly variable, relating to adaptation to aquatic habitat and hygrophilous niches. The characters that separate this species from Cratoneuron filicinum are its slender plants, straight, rarely curved stems and branches, sparse rhizoids, the absence of paraphyllia, the erect, involute leaves, and the elongate-rhomboidal leaf cells (6–10 times as long as wide).